The Advanced Television Systems Committee (ATSC) published a Digital Television Standard in 1995 as Document A/53, hereinafter referred to simply as “A/53” for sake of brevity. Annex D of A/53 titled “RF/Transmission Systems Characteristics” is of particular relevance to this specification, defining many of the terms employed herein. In the beginning years of the twenty-first century, efforts were made to provide for more robust transmission of data over broadcast DTV channels without unduly disrupting the operation of so-called “legacy” DTV receivers already in the field. These efforts culminated in an ATSC standard directed to broadcasting data to mobile receivers being adopted on 15 Oct. 2009. This standard, referred to as “A/153”, is also relevant to this specification, defining many of the terms employed herein. The data for concatenated convolutional coding (CCC) are commonly referred to as “M/H data” in reference to the mobile and handheld receivers that will receive such data.
Both A/53 and A/153 are directed to 8-VSB signals being used in DTV broadcasting. A radio-frequency (RF) 8-VSB signal is transmitted by vestigial-sideband amplitude modulation of a single carrier wave in accordance with an 8-level modulating signal that encodes 3-bit symbols descriptive of 2-bit symbols of the digital data to be transmitted. The three bits in the 3-bit symbols are referred to as Z-sub-2, Z-sub-1 and Z-sub-0 bits. The initial and final bits of each successive 2-bit symbol of the digital information are referred to as an X-sub-2 bit and as an X-sub-1 bit, respectively. The X-sub-2 bits are subjected to interference-filter pre-coding to generate the Z-sub-2 bits, which Z-sub-2 bits can be post-comb filtered in a DTV receiver to recover the X-sub-2 bits. The Z-sub-1 bits correspond to the X-sub-1 bits. The Z-sub-0 bits are redundant bits resulting from one-half-rate convolutional coding of successive X-sub-1 bits to provide two-thirds-rate trellis coding as prescribed by A/53.
A/153 prescribes serial concatenated convolutional coding (SCCC) of data transmitted to mobile receivers, which SCCC uses one-half-rate outer convolutional coding of such data followed by symbol-interleaving and two-thirds-rate trellis coding similar to that prescribed by A/53. The one-half-rate convolutional coding incorporated within the two-thirds-rate trellis coding serves as one-half-rate inner convolutional coding in the SCCC. A/153 further prescribes additional forward-error-correction coding of the data transmitted to mobile receivers, which additional FEC coding comprises transverse Reed-Solomon (TRS) coding combined with lateral cyclic-redundancy-check (CRC) codes which a receiver can use to locate byte errors for the TRS coding. The principal design task for the transverse Reed-Solomon (TRS) coding used in the RS Frames prescribed by A/153 is overcoming drop-outs in received strength caused by reception nulls when the receiver is moved through an electromagnetic field subject to multipath signal propagation. The strongest TRS codes prescribed by A/153 can overcome momentary drop-outs in received signal strength that are as long as four tenths of a second. Furthermore, the shortened 255-byte Reed-Solomon (RS) codes used for TRS coding are very powerful codes for correcting shorter burst errors, especially when used together with codes for locating byte-errors.
A/153 prescribes that the M/H-service information be subjected to outer convolutional coding and symbol interleaving before encapsulation in 188-byte transport-stream (TS) packets called “MHE packets” that are subjected to non-systematic (207, 187) Reed-Solomon coding to generate selected segments of 8-VSB data fields. These segments of 8-VSB data fields are time-division multiplexed with other segments generated by systematic (207, 187) Reed-Solomon coding of 188-byte TS packets of main-service information. The bytes of the resulting 8-VSB data fields are convolutionally interleaved before being subjected to the 2/3 trellis coding that functions as inner convolutional coding of the SCCC used for transmissions to M/H receivers. All the segments of 8-VSB data fields have (207, 187) Reed-Solomon coding to insure that DTV receivers already in the field continue to receive main-service information usefully. Some of those “legacy” DTV receivers might otherwise place themselves in a “sleeping” mode if their decoders for (207, 187) R-S coding find too many of the segments of 8-VSB data fields to contain byte errors that cannot be corrected.
The SCCC used for transmissions to M/H receivers appear in sixteen successive M/H Slots in each of five sub-frames of M/H Frames, which M/H Frames span twenty 8-VSB data frames—i.e., forty 8-VSB data fields. The data occupying an M/H Slot are referred to as an M/H Group. The allocation and assignment of M/H Groups in an M/H Frame is illustrated in FIG. 1 of the drawings. The number of M/H Groups allotted per M/H Frame is a multiple of five, and the Group allotment and assignment are identical for all M/H Sub-Frames in an M/H Frame.
Before convolutional byte interleaving of 8-VSB data fields, an M/H Slot consists of 156 data segments of 8-VSB signal. An M/H Slot may convey just 156 legacy transport-stream (TS) packets, or may be assigned to convey a Group of 118 M/H-carrying MHE packets plus 38 legacy TS packets. The lower row of FIG. 1 illustrates the order in which M/H Groups are assigned to M/H Slots within each M/H sub-Frame as the amount of M/H data increases. Once the assignment is made, however, the M/H data are transmitted in time order of available M/H Slots. For example, if there are 3 M/H Groups per M/H Sub-Frame, then the first Slot (Slot #0), the 5th Slot (Slot #4) and the 9th Slot (Slot #8) will be allocated in each M/H Sub-Frame, shown as Group assignment order numbers 0, 1, and 2. The assignments begin with one-of-four spacing until those possibilities are exhausted, then go to one-of-two, and so on.
An M/H Parade is a collection of related M/H Groups contained within one M/H Frame. An M/H Parade conveys data from one or two particular RS Frames depending on an RS Frame mode. The RS Frame is temporarily stored in a packet-level memory that supports error-correction decoding of the M/H data as transmitted with transverse Reed-Solomon (TRS) coding combined with lateral CRC codes. Each RS Frame carries, and FEC encodes, an M/H Ensemble, which is a collection of M/H services providing the same quality of service (QoS).
The portion of a Parade within a Sub-Frame consists of a collection of consecutively numbered M/H Groups. The structure of a Parade in terms of its constituent Group numbers and Slot numbers within a Sub-Frame is replicated in all Sub-Frames of an M/H Frame, although the data contents of the Groups differ in successive ones of the Sub-Frames. The beginning Group number for the first Parade to which Group numbers are assigned shall be zero. The beginning Group number of a succeeding Parade shall be the next higher Group number after the Group numbers for all preceding Parades have been assigned. The Number of Groups per M/H Sub-Frame (NoG) for an M/H Parade is allowed to range from 1 to 8. Therefore the number of Groups per an M/H Frame for a Parade ranges from 5 to 40 in steps of 5.
In March 2011 Roy Oren of Siano Mobile Silicon reported to ATSC that turbo decoding of a Parade with five Groups per Sub-Frame of an M/H Frame was problematic, if the first of the five numbered Groups in each Sub-Frame were located in Slot #2 thereof. The last of the five Groups in each Sub-Frame would then be located in Slot #1 thereof. Since the M/H Group 8 in Slot #1 was immediately succeeded by the M/H Group 4 in Slot #2, the decoder for the M/H-service SCCC had too little time to carry out iterative decoding procedures on M/H Group 8 fully before M/H Group 4 was received. These iterative decoding procedures are commonly referred to as “turbo decoding” procedures, irrespective of whether the concatenated convolutional coding (CCC) is the type known as “serial concatenated convolutional coding” (SCCC) or an earlier-known other type known as “parallel concatenated convolutional coding” (PCCC). A. L. R. Limberg subsequently reported that a condition of too little time to carry out iterative decoding procedures fully would obtain whenever a Parade composed of more than four Groups per Sub-Frame of an M/H Frame was located so as to include M/H Groups #7 and #8 in each Sub-Frame.
Decoding CCC using a plurality of time-interleaved decoders has been known per se for some time in the prior art. For example, such decoding is described in U.S. Pat. No. 7,827,473 issued 2 Nov. 2010 to Tak K. Lee and Ba-Zhong Shen, titled “Turbo decoder employing ARP (almost regular permutation) interleave and arbitrary number of decoding processors” and assigned to Broadcom Corporation. The general thrust of the prior art is the use of interleaved separate concatenated convolutional coding systems to overcome burst noise. Accordingly, the extent of interleaving in the prior art tends to be smaller or at least no larger than the fields of data being processed. This permits a receiver to use a reasonably small amount of memory to implement de-interleaving during decoding.
The amount of memory that an M/H receiver employs for temporarily storing RS Frames of data recovered as turbo decoding results from an M/H Frame is very large, large enough to store the data packets recovered from five M/H Groups or a multiple up to eight thereof. The data recovered as turbo decoding results from respective ones of the Groups are successively written M/H Group by M/H Group on a time-interleaved basis into the memory for temporarily storing the RS Frame.